Boiler running without a call for heat

mo8414

I have both zones turned off and I noticed my boiler kicked on and opens the zone valve for one of my zones. Even with that zones thermostat taken off its mounting base it still runs so I'm thinking maybe it is the aquastate?

I replaced the L8148j1009 aquastate in February so I'm hoping its not defective but with no other change to the system and me removing the thermostat from its base, the aquastate is probably the culprit.

What are the testing procedures I need to follow with my multimeter to varify how everything is working?

Thanks in advance.

Jamie Hall

It should work the other way around. The thermostat opens the zone valve, and the zone valve requests the boiler. The aquastat will run the boiler — or not — depending on whether the boiler is hot enough.

What you need to do is to disconnect the wires from the thermostat at the zone valve and see if the zone valve closes. It should… If it doesn't, there's a problem in the wiring, assuming the thermostat is off its base.

EdTheHeaterMan

To understand how a thermostat works you need to understand how a light switch works.  When the switch connects the two wires that are connected to the switch, the circuit is completed and the light will illuminate  

Same is true of a thermostat.  When the room temperature drops the thermostat is a switch that turns on the heating system.  When the room gets hotter, the thermostat turns off the switch.  

If for some reason you get the wires to connect when the switch is open (OFF) The lightbulb does not know the switch is off. The light bulb only knows that the electric circuit is complete.  I would look for the wire or thing that is completing the circuit to the zone valve that is open when that zone thermostat is not calling    

HVAC PRO: "How long have you experienced this problem?"

Customer: "Since last Thursday"

Wife: "The day after you hung the new television on the wall"

Customer: "What does hanging the television on the wall have to do with the heater?"

HVAC PRO: "Let me look at that television bracket on the wall"

If you don't get it by now, then you need to hire a pro before you point the parts canon at the problem.

mo8414

Ok im going to find some time to look at it today after work. Im just glad its summer so I don't have to rush it. I'll keep you guys updated, Thanks for all the help.

abro42

Hi and Hello:

A really great explanation from an authority. i also have the same problem. Thermostat shows "NO Call for Heat" for the specific ZONE or ZONES and boiler starts a heating cycle. The TACO Controller ZONE RED LED is ON and boiler starts its cycle for firing after all pre-purge intervals. I need to troubleshoot this as indicated starting at the thermostat and next troubleshoot the TYCO controller. Here is some data I have collected:

(a) Honeywell Aquastat is set for 140 deg LOW and 180 deg HI.

(b) New burner Carlin Ignition Controller installed recently and TT is shorted at the terminal strip. The burner technician (pretty experienced) says he uses all DEFAULT values yet I chose to change TT SHORTED=YES.

(C) Radiant heating is new to me but incredibly nice with warm floors, 3/8 in tubing (old system, wish I had 1/2 in tubing), under subfloor installation w/ alum plates, 2 in radiate barrier, and R-19 installed facing cellar floor. This was a labor-intensive task, but my thermodynamics theory told me this was necessary.

(d) Buderus boiler. I am told the best. No HOT WATER heating, just radiant floor application.

Thank you for your explanation. I will do troubleshooting and report back. Love this forum.

Alan Brosz

Vernon, VT 05354

EdTheHeaterMan

Taco and Honeywell make more than just one control. Let me guess: your Honeywell control is an L8124-type control. The A, B, or other letter in the sixth position will tell us more about that particular control.

As far as the Taco control is concerned, does the model number start with a Z or an R? If it starts with the letter Z, then you have zone valves, and the red light indicates that the end switch is closed, meaning the valve is in the open position.

If the red light is on on either control, that indicates a call for heat. Therefore, the thermostat wires may be connected in some fashion, either intentionally or unintentionally, as in the example of the screw or nail connecting the wires above.

@abro42, to start the problem diagnosis you remove a wire from the Taco Zone thermostat that you believe should not be calling for heat. If the call for heat stops then the Taco control is operating properly and the problem is related to the thermostat and wire connecting it to the Taco Control.

EdTheHeaterMan

@abro42 said "(d) Buderus boiler. I am told the best. No HOT WATER heating, just radiant floor application."

Since you have a setting for Low on your aquastat then you have something that will give your Domestic Hot Water (DHW) priority. I know you said there is no DHW connected to your Buderus boiler, but the control does not care. the control that is set 140° Low Limit means that the circulator (if it is connected to C1 and C2) will not operate unless the boiler water temperature is above 140° so the DHW will have priority. That control also maintains a minimum water temperature of 140° so the DHW is always available when you open the hot water tap.

Now all this does not make sense to you because your hot water is not connected to your Buderus. Just think about how your Buderus feels about it. Working hard to keep the hot water ready for you and you don't even care. You should disconnect that DHW priority function and let it just make heat. Your Buderus will reward you with a lower fuel bill if you do that. Ask me how if you are interested. But you need to tell me the full model number of your Honeywell control